[Feature] Add query metadata comments

[DerekTBrown]

Problem Statement

Database monitoring and tracing tools (ex. Datadog) rely on metadata comments to trace SQL statements. I am looking for an easy way to inject these into SQLC-generated statements, improving traceability and auditability of SQL queries.

Proposal

This adds a query_comments config block that prepends generated SQL with structured metadata comments in either sqlcommenter or marginalia format based on the tags specified in the SQLC comment:

version: "2"
sql:
  - schema: "schema.sql"
    query_comments:
      enabled: true
      format: "sqlcommenter"
      tags:
        - name
        - filename

All generated SQL statements will then contain the tracking comment:

/*sqlc_name='GetAuthor',sqlc_filename='query.sql'*/
-- name: GetAuthor :one
SELECT id, name FROM authors WHERE id = $1

[kyleconroy]

@DerekTBrown please open up an issue or a discussion with your feature request before submitting any code. Thanks.